Burner safety control system



July 5, 1966 3 :5 'L LIJ F I 6. 2 64 R. B. MATTHEWS BURNER SAFETY CONTROL SYSTEM Filed March 24, 1964 6E- EL INVENTOR RUSSELL BMATTHEWS K. M. LEFEVER ATTORNEY United States Patent 3,259,169 BURNER SAFETY CONTROL SYSTEM Russell 18. Matthews, ()conomowoc, Wis., assignor to Penn Controls, Inc., Goshen, Ind., a corporation of Indiana Filed Mar. 24, 1964, Ser. No. 354,353 6 Claims. (Cl. 158-28) This invention relates to control systems and particu larly to control systems for fluid fuel equipment and the like. More particularly the invention relates to control systems havingan automatic purge period which, unlike previous systems, is dependent upon the cooling time of a control device. Still more particularly the invention relates to control systems for gas burning equipment having automatic recycling ignition means to ignite a pilot burner and having an automatic purge period which is dependent upon the cooling time of a warp switch.

In many types of gas burning equipment which is remotely located, such as suspended unit heaters, roof type installations, duct heaters and the like, it is desirable for convenience to have a control system which includes an automatic recycling ignition means to re-ignite the pilot burner in case it becomes extinguished. This feature may be hazardous in some systems due to collection of unburned gas in the combustion zone from the pilot or main burner during the time it takes a flame sensing means to detect the absence of flame and to shut off the gas supply. Since actuation of the flame sensor ordinarily activates the ignition means, any collected gas will ordinarily ignite at this time, causing an explosion in the combustion zone.

The instant invention is directed to the elimination of this problem; toward furnishing a control system which includes an automatic purge period between the time of actuation of the flame sensor to stop flow of fuel to the combustion zone and activation of the ignition system. As an added novel feature the automatic purge period of the control system of the invention is based on the cooling time of a warp switch. By this arrangement the purge period is completely independent of any electrical current variation, and the like.

One object of the invention, therefore, is to provide a control system for liquid fuel combustion equipment having automatic recycling ignition means and an automatic purge period.

A further object of the invention is to provide an automatic control system with an automatic purge period which is dependent upon the cooling time of a warp switch.

Other objects will become evident as the description proceeds.

The invention will be more clearly explained by reference to the accompanying drawings in which FIG. 1 represents a schematic diagram of one embodiment of the invention;

FIG. 2 represents a schematic diagram of a second embodiment of the inventive concept; and

FIG. 3 depicts still another modification of the inventive concept.

Turning now to FIG. 1 reference numeral 2 designates a line switch in line 3, one side of a source of electrical potential, for positive control of the system. Reference numeral 4 designates a flame switch, here a thermocouple relay comprising a single pole double throw switch having a relay coil 5, a flame sensor 6, and being mechanically connected to switches 8 and 10. Reference numeral 12 designates the primary coil of an ignition transformer having a secondary 14 and an igniter 16. Reference numeral 18 designates an electroresponsive valve mean which controls a fuel supply to a pilot burner 20. Reference numeral 22 designates a warp switch with a normally 3,259,169 Patented July 5, 1966 closed contact 23, and 24 is a warp switch heater therefor. Reference numeral 26 indicates a specially designed resistance element. Reference numeral 30 designates a warp switch having a normally closed contact 32, a normally open contact 34, and a warp switch heater 36. Reference numeral 38 designates an electro-responsive valve means controlling the supply of fuel to main burner 40 which is disposed in a combustion zone, not shown. Reference numeral 42 designates a thermostat which is located in a controlled space, not shown. Reference numeral 44 designates a high temperature limiting switch which is used to prevent over-heating of the combustion zone and is located in proximity thereto. It will be appreciated that pilot burner 20 is located in igniting relation to main burner 40 and that igniter 16 is disposed in igniting relation to the pilot burner. Flame sensor 6 is disposed in flame sensing relation to both pilot and main burners.

With contact being made by switch 2 current flows through normally closed switch 8, the primary coil 12 of the ignition means, through contact 23, normally closed warp switch 22, normally closed contact 32, and warp switch 30 to line 28. At the same time current flows through electro-responsive valve 18, contact 23, warp switch 22, contacts 32, and warp switch 30 to line 28, thus operating valve 18 and permitting fuel to be supplied to pilot burner 20.

The current flowing through primary 12 of the ignition means induces current in the secondary coil 14 and igniter- 16 is activated, thus igniting pilot 20. Once pilot 20 is burning the flame sensor 6 induces a current through relay coil 5 of thermocouple relay 4 which opens switch 8 and closes switch 10. Current then flows from line 3 to line 28 through switch 10, line 11, and warp switch heater 36.

After the desired period of time, a time period designed into warp switch 30, warp switch 30 breaks contact 32 and closes contact 34. Current then flows through switch 10, high limit switch 44, thermostat 42, thermo-responsive valve means 33, contacts 34 and warp switch 30 to line 28. The actuation of the valve 38 permits fuel to be supplied to burner 40 which is ignited by the pilot 20. Contact between warp switch 30 and contact 34 is maintained by current through warp switch heater 36 which continues so long as switch 10 is closed.

In the event the high limit switch becomes operative and its contacts are broken or the thermostat in the controlled space calls for a decrease in heat supplied, the circuit is broken and current flow through electro-responsive valve 38 is interrupted and the fuel supply to the main burner 40 is shut 01f. In either of these events, a normal sequence of operations, pilot 20 is unaifected, since suificient current flows through electro-responsive valve means 18, warp switch 22, and resistor 26 to hold valve 18 open.

However the resistance of resistor 26 is sutficiently high so that current flow through it is not enough to open valve 18 if in the closed position. Thermocouple relay 4 is still activated by flame sensor 6 to maintain switch 8 open and switch 10 closed. Warp switch heater 36 continues to maintain contacts 34 closed so that when the high limit switch 44 contacts remake or the thermostat 42 calls for more heat the circuit is completed through switch 10, high limit switch 44, thermostat 42, main gas valve 38, contact 34, and warp switch 30 to line 28, and burner 46 lights again.

In the event of a failure of conditions, however, that is' to say, an interruption of the gas supply (which ext-inguishes all flame in the combustion zone), an electrical failure (which interrupts the gas supply by inactivation of the electro-responsive valve means) or the like, the thermocouple relay 4 immediately operates to close switch 8 and open switch 10. This shuts off the gas supply to the main burner 40 and stops the flow of current through warp switch heater 36. Warp switch 30 then starts to cool, breaking contact 34. Until contact 32 is made again, that is, until warp switch 30 has cooled sufficiently to make this contact again, there is no current flow through primary 12 of the igniter, thus preventing the ignition of any collected fuel in the combustion zone. The cooling period of warp switch 30 thus represents a purge time to allow unburned gases to escape from the combustion zone. This cooling period is varied by the design of warp switch 30.

After the desired purge period, that is to say, after warp switch 30 has cool-ed sufliciently to make contact 32, current flows again through switch 8, the primary coil 12 of the ignition means, warp switch 22, contacts 32 and warp switch 30 to line 28. The electro-responsive valve 18 is activated, igniting means 16 ignites the pilot burner 20 and the cycle is repeated.

In the event there is a failure of ignition of pilot 20, due to failure of the fuel supply, failure of the igniter, malfunction of the electro-responsive valve 18, etc, continued current flow through warp switch heater 24 causes warp switch 22 to break contacts 23, thus shutting off the current through thermo-responsive valve 18 .and fuel supply to pilot burner 20 and the primary coil 12 of the ignition means. This condition persists until the system is serviced.

The system described above is of the 100% shut-E type, that is to say, the fuel supply to the pilot burner is interrupted in the event of a failure of conditions. This type of control system is desirable when a heavy fuel supply such as liquid petroleum gas, etc. is used. In instances where the control system is adapted to lighter fuels the 100% shut-off system is ordinarily not necessary and electro-responsive valve means 18, warp switch 22, contacts 23, and warp switch heater 24 may be eliminated from the system. Pilot burner 20 is then continuously supplied directly from the main fuel supply.

Turning now to a second embodiment of the invention depicted in FIG. 2, reference numerals 50 and 52 designate lines which represent both sides of a source of electrical potential. Interposed in line 50 is line switch 54 for positive control of the system. Reference numeral 56 designates a warp switch having a normally closed contact 58 and a warp switch heater 60. A relay coil 62 is connected by mechanical means 64 to a normally open switch 66 with a contact at 68 and a normally closed switch 70 having a contact 72. Bridging switch 66 and contact 68 is resistor 73, which is specially designed to accomplish the function ascribed to it below.

Ignition means 74 comprises a primary transformer coil 76, a secondary transformer coil 78 and an igniter 80. Reference numeral 82 designates a pilot burner having a source of liquid fuel controlled by electroresponsive valve means 84. Main burner 86 is supplied with fuel through electro-responsive valve means 90.

Reference numeral 92 designates a flame switch, here a thermocouple relay, having a flame sensor 94 and a relay coil 96. Main burner 86 is located in a combustion zone, not shown, and pilot burner 82 is positioned in igniting relation to the main burner. Igniting means 80 is located in igniting relation to pilot burner 82 and flame sensor 94 is positioned so that it will sense the presence of flame from either pilot burner 82 and/or main burner 86.

Relay coil 96 is connected by mechanical means 98 to normally closed switch 100 having a contact 102 and normally open switch 104 having a contact 106 connected directly to line 52.

Reference numeral 108 designates a second warp switch having a normally closed contact 110, a normally open contact 112 and a warp switch heater 113. Reference numeral 114 indicates a thermostat located in a controlled space, not shown, and reference numeral 116 designates a high temperature limiting switch which is positioned to sense the temperature in a combustion zone, not shown.

When line switch 54 is closed and the control system is operative, current flows from line 50 to line 52 through Warp switch 56, contact 58, the primary coil 76 of the ignition means, switch 100, contact 102, warp switch 108, and contact 110. At the same time current flows through warp switch heater 60, relay coil 62, switch 100, contact 102, warp switch 108 and contact 110. The flow of current through relay coil 62 activates this relay and causes switch 70 to open and switch 66 to close. Current then flows through warp switch 56, contact 58, switch 66, contact 68, and activates electro-responsive valve 84, then through warp switch 108 and contact 110. The activation of electro-responsive valve 84 permits the flow of fuel to pilot burner 82. The concurrent flow of electrical current through primary coil 76 induces a current in secondary coil 78 of the igniter 74. The igniter is thus brought to ignition temperature and the fuel flowing from pilot burner 82 is ignited.

The pilot burner flame is sensed by the flame sensor 94 of the thermocouple relay 92 and the current induced through relay coil 96 opens switch and closes switch 104 by mechanical means 98. Opening of switch 100 de-energizes ignition means 74 and relay coil 62. The de-energizing of relay coil 62 results in the mechanical means 64 opening switch 66 and closing switch 70. Closing switch 70 allows current to flow from line 50 through warp switch 56, contact 58, switch 70, contact 72, warp switch heater 113, warp switch 108 and contact 110 to line 52. The flow of current through warp switch heater 113 after the desired time interval which is built in to the warp switch, causes warp switch 108 to break contact 110 and make contact 112. Electrical current then flows from line 50 through electro-responsive valve means 90, high limit switch 116, thermostat 114, contact 112, warp switch 108, switch 104 and contact 106 to line 52. This current flow activates electro-responsive valve means 90 and permits a flow of fuel to main burner 86 which is then ignited by means of pilot burner 82. The normal ignition cycle is thus completed.

In the normal sequence of operations, for example, the high temperature limiting switch indicating an excessive temperature in the combustion zone or the thermostat breaking contact due to an elevated temperature in the controlled space, the current through the electro-responsive valve means 90 is interrupted and the main burners fuel supply is interrupted. The pilot burner remains ignited, however, since sufficient current flows through resistor 73 to maintain the electro-responsive valve means 84 in the open position but not enough to re-open the valve once it is closed. Thus when in the normal sequence of operations the high temperature limiting switch contacts reclose or the thermostat in the controlled space calls for additional heat, the circuit, line 50, electro-responsive valve means 90,. high temperature limiting switch 116, thermostat 114-, contact 112, warp switch 108, switch 104, contact 106, and line 52 is completed again. During the interruption of this circuit, however, warp switch 108 is held in position of contact with 112 by the continued flow of current through warp switch heater 113 via warp switch 56, contact 58, switch 70 and contact 72.

Upon a failure of conditions, however, that is to say, an interruption in the source of electrical potential, an interruption of the fuel supply to the main burner or to the pilot burner the following sequence of operations occurs.

The absence of flame in the combustion zone is sensed by flame sensor 94 and thermocouple relay 92 opens switch 104 and closes switch 100. During the continued failure of electrical power the system remains in this condition until serviced.

If the interruption in the electrical power is momentary, resumption of the potential has no effect upon the system until warp switch 108 has completed its cooling period and remade contact 110. The cooling period of warp switch 108 may be varied as desired and this cooling period represents the safety feature of this embodiment of the invention.

The same situation is brought about in case of a flameout in the combustion zone; that is to say, a momentary interruption in the fuel supply to the main burner and pilot burner. The absence of a flame is detected by flame sensor 94 and relay coil 96 opens switch 104 closing switch 100. No circuit is completed however until warp switch 108 cools to its original position making contact 110. When this contact is made the ignition circuit of line 50, warp switch 56, contact 58, primary ignition coil 76, switch 100, contact 102, warp switch 108, contact 110 and line 52 is completed and the system repeats the operation as described above.

In the event, during the ignition cycle, pilot burner 82 fails to light, the continued flow of current through warp switch heater 60 causes warp switch 56 to break contact 58 and the control system remains inoperative until serviced.

In FIG. 3 there is depicted a third embodiment of the inventive concept which does not have the 100% shutoff features of the embodiments shown in FIGS. 1 and 2. In this system reference numerals 118 and 120 designate lines which represent both sides of a source of electrical potential. Line switch 122 for positive control of this system is interposed in line 118. Reference numeral 124 designates ignition means having a primary coil 126, a secondary .coil 128 and an igniter 130. Reference numeral 132 indicates a flame switch, here a thermocouple relay having a flame sensor 134 and a relay coil 136. Mechanical means 138 is connected to a normally closed switch 140 having a contact 142 and a normally open switch 144 having a contact 146. Reference numeral 148 designates a Warp switch having a normally closed contact 150, a normally open contact 152 and a warp switch heater 154. A thermostat located in a con trolled space, not shown, is designated by reference numeral 156. 'A high temperature limiting switch located in proximity to a combustion zone, not shown, is designated by reference numeral 158. Reference numeral 160 designates an electro-responsive valve means controlling fuel supply to a main burner 162 located in the combustion zone. Pilot burner 164, also located in the combustion zone and in igniting relation to main burner 162, is supplied directly from the main fuel supply. Igniter 130 is located in igniting relation to pilot burner 164 and flame sensor 134 is positioned so as to detect the presence of flame from either the pilot burner 164 or main burner 162.

In this system the flw of current from line 118 to line 120 is initially through primary igniter coil 126, switch 140, contact 142, warp switch 148 and contact 150 to line 120. The flow of current through primary coil 126 induces a current in the secondary coil 128 and activates igniter 130 which causes ignition of the pilot burner 164. The presence of flame is detected by flame sensor 134 and the thermocouple relay 132 is activated opening switch 140 and closing switch 144. Opening switch 140 shuts off the current through the igniter. At the same time current flows from line 118 through warp switch heater 154, warp switch 148, and contact 150 to line 120. When the temperature of warp switch 148 is elevated by warp switch heater 154 enough to break contact 150, that is to say, after the design period of the warp switch, current continues to flow through warp switch heater 154 through switch 144 and contact 146 to line 120. When warp switch 148 is warped sufliciently to make contact 152 it is held in this position by current flowing through the circuit just described. Additionally a circuit is completed from line 118 through electro-responsive valve means 160, high limit switch 158, thermostat 156, contact 152, warp switch 148, switch 144, and contact 146, to

line 120. Current through electro-responsive valve means 160 activates this valve and permits the flow of fuel to main burner 162, which is then ignited by pilot burner 164.

In the normal sequence of operations, which would include the opening of the high limit temperature switch or the contacts of the thermostat in the controlled space, the circuit through the electro-responsive valve means 160 is interrupted and the supply of fuel to the main burner is shut off. The thermocouple relay 132 is held in its existing position by the presence of flame from pilot burner 164. Therefore, when the high temperature limit switch closes or the thermostat contact is again made, the circuit through thermo-responsive valve means 160 is again completed and fuel is again supplied to the main burner and is ignited by the pilot burner 164.

When a total flame-out occurs, however, the absence of flame is detected by thermocouple relay 132 and switch 144 is opened and switch 140 is closed immediately. This breaks all circuits, shutting 01f the fuel to the main burner and preventing the igniter from lighting the pilot burner. The control system remains in this condition until warp switch 148 cools sufliciently to remake contact 150. During this cooling time, which is designed into warp switch 148, any gases in the combustion zone are purged with the exception of the gas from pilot burner 164 which is normally of an insignificant amount when using high volatility fuels. Once warp switch 148 has passed through its cooling period and contact is reestablished with contact 150, current again flows from line 118 through the primary coil 126 of the igniter 124, switch 140, contact 142, warp switch 148, and contact 150 to line 20. This brings about the ignition of pilot burner 164 in a manner described above and the cycle re-occurs.

Those familiar with the art will recognize that various modifications may be incorporated into the concept described above without any material variance therefrom.

- For example, the ignition means described may be of the glow coil type such that igniter 16 is of a high resistance wire and secondary 14 furnishes approximately 2.5 volts to activate the igniter. The ignition means may be of the spark coil type with as high as 10,000 volts on secondary 14.

It is also obvious that the electrical potential described is preferably of low voltage e.g. 24-26 volts which may be supplied by a transformer wherein the primary coil draws from to 270 volts.

It is also contemplated that the flame sensing means may include, in addition to the thermocouple relay with the single pole double throw switch specifically described above, any thermo-electric operated device or flame responsive switch known to the art. For example a thermopile, a bi-metal or differential expansion type flame switch may be designed into the control system of this invention.

To review =briefly the instant invention relates to fluid fuel control systems. Particularly the invention relates to control systems for fluid fuels wherein a failure of condition results in inactivation of ignition means for a period of time which is dependent upon the design of a thermo-responsive device. instant invention, then, incorporates a purge period wherein the duration of the period is dependent upon the cooling time of a warp switch.

The invention comprises a control system which includes a main burner and a pilot burner which is disposed in a combustion zone, and ignition means disposed in igniting relation to the pilot burner in the combustion zone. Also responsive to the combustion zone there is a flame switch which when activated, opens a first switch, normally closed, located in a first circuit, and closes a second switch, normally open, in asecond circuit. In the first, normally closed circuit, there is a primary coil of a transformer ignition means, a normally The control system of the.

closed first warp switch, an electro-responsive valve means controlling fuel supply to a pilot burner and a normally closed second warp switch.

In the second circuit, and the one which is made by actuation of the flame switch, there is a high limit switch, a thermostat, an electro-responsive valve for controlling fuel to the main burner and a warp switch heater for controlling the temperature of the warp switch of the first circuit.

The gist of the invention resides in a division of the electrical current of the circuit about the two contacts of the second warp switch. When the warp switch is completing the first circuit there is no fuel supplied to the main burner. When the warp switch completes the second circuit, the ignition means normally has been inactivated. In changing from the second circuit back to the first circuit re-energization of the first circuit is delayed by the cooling time of the warp switch and during this cooling time there is no fuel supplied to the main or pilot burners nor is there ignition means available. Thence the combustion zone has a designed period of time within which to purge itself of raw or unburned gases.

It is understood, of course, that various modifications of the concept described above may be apparent to those skilled in the art. It is intended that the disclosure is considered to be non-restrictive and that the inventive concept should be interpreted as broadly as allowed by the scope of the appended claims.

What is claimed is:

1. A fuel and ignition control system which comprises the following elements:

a main fuel burner located in a combustion zone,

electro-responsive valve means for regulating the flow of fuel to said burner,

a pilot burner disposed in igniting relation to said main fuel burner,

electro-responsive valve means for regulating the flow of fuel to said pilot burner,

igniting means electrically actuated and disposed in igniting relation to said pilot burner,

a flame switch disposed in flame detecting relation to said burners and operatively connected to a first normally closed switch and a second normally open switch,

a first thermo-responsive switch having a normally closed first contact and a normally open second contact,

a thermal device for actuation of said first thermoresponsive switch,

a second thermo-responsive switch having a normally closed contact,

a thermal device for actuation of said second thermoresponsive switch,

an electro-responsive relay operatively connected to a first normally closed switch and a second normally open switch,

a resistance element bridging said first normally closed switch,

circuit means operatively connecting said elements to each other and to a source of electrical potential so that the flow of electric current through said second thermo-responsive switch and said first normally closed switch of said electro-responsive relay actuates said electro-responsive valve means to permit a flow of fuel to said pilot burner and a concomitant flow of electric current through said igniter ignites said pilot burner,

the flame switch actuated by the flame from said ignited pilot burner opening said normally closed first switch and closing said normally open second switch,

the opening of said normally closed first switch interrupting the flow of electric current through said electro-responsive relay and causing said first normally closed relay switch to open and said second normally open relay switch to close whereupon current continues to flow through said electro-responsive valve means, regulating the flow of fuel to said pilot burner through. said resistance element holding it in the open position and allowing current to flow through said thermal device of said first thermo-responsive switch thereby actuating said switch to open said first normally closed contact and close said second normally open contact, the closing of the second contact permitting the flow of electric current to actuate said electro-responsive valve means allowing a flow of fuel to said main burner which is ignited by said pilot burner,

the elements also being operatively connected so that the absence of flame from said burners actuates said flame switch so as to interrupt the flow of electric current through said igniter, both electro-responsive valve means, and said thermal device for said first thermo-responsive switch for a period of time sufficient to purge any unburned fuel from said combustion zone.

2. A control system according to claim 1 wherein said flame switch is a thermocouple relay having a single pole double throw switch.

3. A control system according to claim 1 wherein said thermo-responsive switches are warp switches and wherein said thermal devices are warp switch heaters.

4. A fuel and ignition control system which comprises the following elements:

a main fuel burner located in a combustion zone,

electro-responsive valve means for regulating the flow of fuel to said burner,

a pilot burner disposed in igniting relation to said main burner,

electro-responsive valve means for regulating the flow of fuel to said pilot burner,

igniting means disposed in igniting relation to said pilot burner,

a flame switch disposed in flame detecting relation to said main burner and said pilot burner,

a first normally closed switch and a second normally open switch mechanically operated by said flame switch,

a first thermo-responsive switch having a first normally closed contact and a second normally open contact,

a thermal device disposed in actuating relation to said first thermo-responsive switch,

a second thermo-responsive switch having a single normally closed contact,

a thermal device disposed in actuating relation to said second thermo-responsive switch,

an electrical resistance element disposed in series relationship with said second thermo-responsive switch,

circuit means operatively connecting said elements to each other and to a source of electrical potential such that the flow of electrical current through said thermo-responsive valve means regulating the flow of fuel to said pilot burner actuates said valve permitting a flow of fuel to said pilot burner and a concomitant flow of electrical current through the first normally closed switch of said flame switch actuates said igniter to ignite the fuel flowing from said pilot burner and whereby the flame switch detecting the presence of flame at said pilot burner is actuated to open said first normally closed switch and to close said second normally open switch, thus permitting electrical current to flow through said thermal device of said first thermo-responsive switch, the opening of said first normally closed switch of said flame switch interrupting the flow of current through said igniter, the flow of current through said thermo-responsive valve means relating the flow of current to said pilot burner holding said valve means in the open position by the flow of current through said resistance element, the flow of current through the said thermal device of said first thermoresponsive switch actuating said switch to open said first normally closed contact and cause said second normally open contact to close whereby the electrical current is allowed to flow through said thermoresponsive valve means regulating the flow of fuel to said main burner and allowing fuel to be supplied to said main burner, said fuel being then ignited by said pilot burner, said elements also being operatively related '50 as to maintain said igniter in an inactive state for a period of time during which said first thermo-responsive switch breaks said second contact and re-makes said first contact, thus allowing any uncombusted fuel to escape from said combustion zone.

References Cited by the Examiner UNITED STATES PATENTS Kerr 158-128 Bower 15828 Jones 158-28 Bredesen et al. 15828 15 JAMES w. WESTHAVER, Primary Examiner. 

1. A FUEL AND IGNITION CONTROL SYSTEM WHICH COMPRISES THE FOLLOWING ELEMENTS: A MAIN FUEL BURNER LOCATED IN A COMBUSTION ZONE, ELECTRO-RESPONSIVE VALVE MEANS FOR REGULATING THE FLOW OF FUEL TO SAID BURNER, A PILOT BURNER DISPOSED IN IGNITING RELATION TO SAID MAIN FUEL BURNER, ELECTRO-RESPONSIVE VALVE MEANS FOR REGULATING THE FLOW OF FUEL TO SAID PILOT BURNER, IGNITING MEANS ELECTRICALLY ACTUATED AND DISPOSED IN IGNITING RELATION TO SAID PILOT BURNER, A FLAME SWITCH DISPOSED IN FLAME DETECTING RELATION TO SAID BURNERS AND OPERATIVELY CONNECTED TO A FIRST NORMALLY CLOSED SWITCH AND A SECOND NORMALLY OPEN SWITCH, A FIRST THERMO-RESPONSIVE SWITCH HAVING A NORMALLY CLOSED FIRST CONTACT AND A NORMALLY OPEN SECOND CONTACT, A THERMAL DEVICE FOR ACTUATION OF SAID FIRST THERMORESPONSIVE SWITCH, A SECOND THERMO-RESPONSIVE SWITCH HAVING A NORMALLY CLOSED CONTACT, A THERMAL DEVICE FOR ACTUATION OF SAID SECOND THERMORESPONSIVE SWITCH, AN ELECTRO-RESPONSIVE RELAY OPERATIVELY CONNECTED TO A FIRST NORMALLY CLOSED SWITCH AND A SECOND NORMALLY OPEN SWITCH, A RESISTANCE ELEMENT BRIDGING SAID FIRST NORMALLY CLOSED SWITCH, CIRCUIT MEANS OPERATIVELY CONNECTING SAID ELEMENTS TO EACH OTHER AND TO A SOURCE OF ELECTRICAL POTENTIAL SO THAT THE FLOW OF ELECTRIC CURRENT THROUGH SAID SECOND THERMO-RESPONSIVE SWITCH AND SAID FIRST NORMALLY CLOSED SWITCH OF SAID ELECTRO-RESPONSIVE RELAY ACTUATES SAID ELECTRO-RESPONSIVE VALVE MEANS TO PERMIT A FLOW OF FUEL TO SAID PILOT BURNER AND A CONCOMITANT FLOW OF ELECTRIC CURRENT THROUGH SAID IGNITER IGNITES SAID PILOT BURNER, THE FLAME SWITCH ACTUATED BY TEH FLAME FROM SAID IGNITED PILOT BURNER OPENING SAID NORMALLY CLOSED FIRST SWITCH AND CLOSING SAID NORMALLY OPEN SECOND SWITCH, THE OPENING OF SAID NORMALLY CLOSED FIRST SWITCH INTERRUPTING THE FLOW OF ELECTRIC CURRENT THROUGH SAID ELECTRO-RESPONSIVE RELAY AND CAUSING SAID FIRST NORMALLY CLOSED RELAY SWITCH TO OPEN AND SAID SECOND NORMALLY OPEN RELAY SWITCH TO CLOSE WHEREUPON CURRENT CONTINUES TO FLOW THROUGH SAID ELECTRO-RESPONSIVE VALVE MEANS, REGULATING THE FLOW OF FUEL TO SAID PILOT BURNER THROUGH SAID RESISTANCE ELEMENT HOLDING IT IN THE OPEN POSITION AND ALLOWING CURRENT TO FLOW THROUGH SAID THERMAL DEVICE OF SAID FIRST THERMO-RESPONSIVE SWITCH THEEBY ACTUATING SAID SWITCH TO OPEN SAID FIRST NORMALLY CLOSED CONTACT AND CLOSE SAID SECOND NORMALLY OPEN CONTACT, THE CLOSING OF THE SECOND CONTACT PERMITTING THE FLOW OF ELECTRIC CURRENT TO ACTUATE SAID ELECTRO-RESPONSIVE VALVE MEANS ALLOWING A FLOW OF FUEL TO SAID MAIN BURNER WHICH IS IGNITED BY SAID PILOT BURNER, THE ELEMENTS ALSO BEING OPERATIVELY CONNECTED SO THAT THE ABSENCE OF FLAME FROM SAID BURNERS ACTUATES SAID FLAME SWITCH SO AS TO INTERRUPT THE FLOW OF ELECTRIC CURRENT THROUGH SAID IGNITER, BOTH ELECTRO-RESPONSIVE VALVE MEANS, AND SAID THERMAL DEVICE FOR SAID FIRST THERMO-RESPONSIVE SWITCH FOR A PERIOD OF TIME SUFFICIENT TO PURGE ANY UNBURNED FUEL FROM SAID COMBUSTION ZONE. 